The present disclosure is related to methods of forming a fine-featured printed layer such as in semiconductor device manufacturing, and more specifically to methods and apparatus employing a print-patterned phase-change material for region masking during material deposition.
There are today many well-known processes for selective material deposition in wafer processing, such as in the manufacture of patterned layers in semiconductor wafer processing. One such process of interest herein is referred to as a liftoff process. In a typical liftoff process, a resist structure is formed over a region of a wafer in order to block the deposition of material in that region. The material of interest is then deposited over at least portions of the wafer, including over the resist structure. The resist structure is then dissolved for example by a solvent, removing both the resist structure and the material of interested deposited thereover. In this way, a definition of a pattern on the wafer surface may be obtained without etching. Since the liftoff process is an alternative to the more common photolithographic etching processes, the liftoff process is often used to define geometry of materials which are difficult to etch, such as gold.
One requirement for a liftoff process is that in the process of forming the resist structure, means for introducing the solvent underneath the deposited material of interest must be provided so that the solvent may dissolve the underlying resist structure. This typically requires that the resist structure be taller (i.e., thicker) than the thickness of the deposited layer of material of interest. Furthermore, the resist structure is typically patterned during or after deposition so that the solvent may contact as much of the resist structure as possible and so that it dissolves the resist structure as quickly as possible, for example by providing the resist structure with re-entrant sidewalls. An example of a structure used in this process is illustrated in FIGS. 7A and 7B. With reference to FIG. 7A, substrate 50 has formed thereon a resist structure 54, patterned to have reentrant sidewalls, and a target material layer 56 formed thereover such that a first portion 56a overlies resist structure 54 and a second portion 56b directly overlies the substrate 52 (or alternatively, intermediate layers, not shown). A solvent may be introduced into regions 58 due to the reentrant sidewall profile of resist structure 54 to thereby dissolve and remove resist structure 54 and with it remove portion 56a of layer 56. The device following the liftoff step is shown in FIG. 7B.
While liftoff is an effective process for wafer patterning, the process has several limitations. First, the resist structure must be formed to be significantly taller than the target material layer, or conversely the thickness of the target layer must be made thin relative to that of the resist structure. Second, the resist structure must be patterned during or after deposition so as to have a reentrant sidewall profile. Each of these limitations result in a relatively high cost and complexity of this wafer patterning process. Furthermore, there is a limit to the width of a useful resist structure and hence to the width of the masked region. If the mask structure is too wide, the solvent takes a significant time to fully undercut the structure, resulting in unwanted damage to other portions of the structure by the solvent. Thus, there is a need in the art for a process which provides a patterned wafer without requiring etching and without limitations on thickness of a target material layer or width of the masked region.